A computer model to simulate patellar biomechanics following total knee replacement: the effects of femoral component alignment

Objective. The objective of this study is to analyze the biomechanics of the patellar component following total knee replacement. More specifically we investigated the effect of displacing the femoral component of an Insall–Burstein II total knee replacement on the patellar tracking and patello-femoral contact pressures. Design. We used a validated computer simulation of the knee joint to virtually insert the femoral component with the following four types of placements: (1) no misplacement, (2) 5° of internal rotation, (3) 5° of external rotation and (4) 5° of flexion rotation. The patellar 3D tracking and patello-femoral contact pressures were computed for each femoral component placement as a function of knee flexion angle. Background. Complications at the patello-femoral joint are the among most frequent following total knee replacement. Results. Femoral component placement unevenly affected the associated patellar tracking: a 5° internal rotation tilted and rotated the patella laterally by about 5° throughout knee flexion. A 5° external rotation of the femoral component had less effect on patellar tracking. A rotation of 5° in flexion primarily caused patellar rotation (5–10° lateral rotation). Femoral component malalignment had only minor effects on the peak pressure distributions at the patello-femoral interface. Conclusion. These results suggest that femoral component positioning primarily affects patellar tracking, with a possible threat for patellar subluxation under external rotation of the femoral component.